Addition-cure silicone compositions, when cured, have many advantages including heat resistance, weathering resistance and chemical resistance and also exhibit good properties of electric insulation, low-temperature behavior, and gas permeability. With respect to mold release, antifoaming and water repellency, they have unique properties which are not observed in other resins. Thus the silicone compositions are used in a wide variety of applications as the coating material that can take advantage of interfacial properties.
The addition-cure silicone compositions which are currently in commercial use generally contain an alkenyl-containing organopolysiloxane as a base, a SiH-containing organohydrogenpolysiloxane as a crosslinking agent, and a metal complex capable of catalyzing addition reaction as a cure catalyst. As to the organohydrogenpolysiloxane, various structures have been proposed. Regardless of whether the structure is linear or branched, those organohydrogenpolysiloxanes having a side chain consisting of polysiloxane units of the following formula (7) and/or (8):
wherein R is an organic group of one or more carbon atoms are most often used. They are generally divided into two classes, organohydrogenpolysiloxanes of the homopolymer structure consisting of units of formula (7) except the terminal groups, and organohydrogenpolysiloxanes of the copolymer structure wherein basic units of formulae (7) and (8) are randomly arranged.
The two classes of organohydrogenpolysiloxanes have different characteristics. The organohydrogenpolysiloxanes of the copolymer structure are more effectively curable. On the other hand, the organohydrogenpolysiloxanes of the homopolymer structure are superior in the adhesion to substrates which is requisite for use as a coating material. Each crosslinking agent has both merits and demerits. There is a need for a crosslinking agent meeting both the functions.